Worn truck tyres are normally retreaded, i.e. the worn tread removed and replaced with a new one. Retreading truck tyres comprises removing the worn tread from the tyre mechanically to expose the casing; applying a new tread to the casing by winding a green-rubber intermediate strip or cushion and a tread strip about the casing; and curing the casing to grip the tread firmly to the casing by means of the bonding action of the cushion.
After removing the worn tread, a lateral surface and/or sidewall of the casing are/is skived manually to remove any existing local damage. This results in the formation of holes and/or craters in the lateral surface of the casing, which, after skiving is completed, are filled manually with green rubber. For the green rubber to grip firmly to the casing, the lateral surface of the casing, before being filled, is sprayed with a liquid (known as cement) comprising green rubber and normalheptane (or other organic solvent), and which serves to prevent detachment of the green rubber from the casing. Statistical studies show that, before being filled, each casing is sprayed on average with roughly 500 grams of cement.
Applying cement has several drawbacks. Being volatile and potentially highly contaminating, cement must be applied in a special cement spray booth, which is bulky, expensive, and normally insulated with rock wool (which involves special, high-cost disposal procedures). Moreover, the cement itself is stored in drums, which also involve special, high-cost disposal procedures; the presence of cement between the casing and the cushion, i.e. of a heterogeneous material between two layers of rubber, may impair performance of the retreaded tyre; and, finally, given the highly contaminating nature of the organic solvents used in cement, avoiding the use of organic-solvent-based cement would greatly reduce the environmental impact of the tyre retreading process as a whole. In this connection, it is important to note that European Union Directive VOC 13/1999/EC calls for a 75% reduction, by the year 2007, in the use of organic solvents in industrial processes with an organic solvent consumption of over 15 tons.